Epoxide compounds have a broad range of uses, particularly in the area of epoxy polymers. Quaternary ammonium epoxide salts (e.g. glycidyl ammonium salts) are commonly used for preparing cationically active cellulosic products such as starches, polyamines, and the like.
Epoxidation methods typically involve dehydrohalogenation of a halohydrin by addition of a base or direct synthesis by reaction with epichlorohydrin. Both methods, however, have drawbacks. Dehydrohalogenation generally results in the production of a mole equivalent of salt as a byproduct which is detrimental to the yield and end use of the epoxide. The presence of sodium chloride (NaCl), for example, can reverse the reaction because the chloride ion may nucleophilically react with the oxirane functionality, resulting in loss of product and lower yield. Waste disposal may become a problem where the salinity of the waste stream is subject to regulation. The use of epoxide solutions having a high chloride concentration is also limited in systems where chloride-based corrosion is a concern. On the other hand, direct synthesis requires use of a large molar excess of the epichlorohydrin, typically as solvent, which then has to be removed. Residual epichlorohydrin can also cause unwanted crosslinking in cellulosic applications.
Removing the salt from the epoxide product has been a major difficulty. One known method involves precipitation from an organic solvent, such as isopropyl alcohol, having miscibility with the epoxide followed by distillation recovery of the product. Large quantities of solvent are required, however, and many epoxides are heat sensitive so that the recovery process can significantly reduce the yield.
Consequently, efforts have been made to produce a low salt epoxide to obviate subsequent salt removal. U.S. Pat. No. 3,335,156 to Smith describes the use of anion exchange resins of the hydroxyl form. These resins are generally unsuitable for commercial scale production because the synthesis is mole-for-mole, thus requiring frequent regeneration of the resin.
Japanese Kokoku No. 63(1988)-4919 describes epoxidation of a halohydrin in an electrochemical cell wherein the salt byproduct is separated from the epoxide product by electrodialysis. A glycidyl ammonium salt is said to be prepared by electrodialysis of an ammonium halohydrin salt produced by a conventional method. The electrodialysis vessel comprises a series of adjacent chambers between a cathode and an anode separated by anionic exchange membranes. The apparatus also comprises alternating charges of either the halohydrin or a hydroxide solution. Anion migration is driven by an electric current into the adjacent chamber toward the anode. In this manner hydroxyl ions migrate into an adjacent halohydrin chamber and react to produce the epoxide, and halogen ions produced by the ring closure migrate toward the anode into the next adjacent hydroxide chamber. In such manner, ion impurities are said to be removed from the epoxide product.
In Japanese Kokoku No. 63(1988)-12148, a similar method is disclosed except that the electrodialysis vessel comprises a series of adjacent chambers between a cathode and anode separated by either anionic or cationic exchange membranes. Chambers charged with hydroxide and an electrolyte solution sandwich a chamber containing a charge of halohydrin. The chamber in the triplet containing the electrolyte solution is closest to the anode. Anionic exchange membranes separate the halohydrin chamber from adjacent chambers and a cationic exchange membrane separates the electrolyte chamber from the hydroxide chamber. When a direct current is imposed, a single direction migration of hydroxyl and halogen anions towards the anode occurs. In this manner, hydroxyl ions are said to migrate into the adjacent halohydrin chamber reacting with the halohydrin to produce the epoxide and halogen ions produced by the dehydrohalogenation reaction are said to migrate into the adjacent electrolyte chamber for removal as a metal salt. Metal ions are said to migrate oppositely (towards the cathode) from the hydroxide chamber through the cation membrane into the electrolyte solution for combination with the halogen ions above.
Use of an electrochemical cell for epoxidizing olefins is described in U.S. Pat. No. 3,723,364 to Leduc; U.S. Pat. No. 4,119,507 to Simmrock et al.; and U.S. Pat. No. 4,126,526 to Kwon et al. Generally, the olefin feed initially reacts with chlorine generated in an anode compartment to produce a chlorohydrin intermediate. Dehydrohalogenation is generally effected by base present in a cathode compartment.
Use of a membrane in an epoxidation process is described in Japanese Patent 60-197,665. A reverse osmosis membrane concentrates olefin halohydrins which are epoxidated by conventional techniques.
Various kinds of Donnan type dialysis processes are generally known in the art. Efficiency is generally the major shortcoming of such methods. Mass transfer must be adequate for the diffusing species; otherwise, the required time and membrane area become unreasonably great. Mass transfer rate for the product species must be low to avoid product losses into the dialysate.
Dialysis diffusion processes are described in several references including U.S. Pat. No. 3,454,490 to Wallace; U.S. Pat. No. 4,306,946 to Kim; and U.S. Pat. No. 4,559,144 to Pfenninger et al.; Japanese Patent 62-190,100; Thomas A. Davies et al., American Institute of Chemical Engineers Journal, Vol. 17, No. 4, Jul. 1971, pp. 1066-1008; and G. Wisniewska et al., Desalination, vol. 56, (1986) pp. 161-173.
Dialysis reaction processes are disclosed in Australian Patent 88-20399; U.S. Pat. No. 4,409,103 to Cremonesi et al.; and European Patent Application 266,059.
Catalytic membrane processes are disclosed in U.S. Pat. Nos. 4,786,597; 4,800,162 (and related PCT 88-07582); U.S. Pat. No. 4,754,089 (and related PCT 88-04286) all to Matson et al.; U.S. Pat. Nos. 4,791,079 and 4,827,071 to Hazbun; and Japanese patent 01-242,401.
An electrodialysis process is described in a paper by K. N. Mani, available from Aquatech Systems of New Jersey entitled "Electrodialysis Water Splitting Technology" wherein various anionic, cationic and bipolar membranes are disclosed to concentrate ions in solution and convert such ions into the acid or base. In this process, dialysis is driven by an electrical potential and water is split.
In the RAIPORE Products Catalog distributed by RAI Research Corp. of New York, dialysis is said to be useful in desalting applications, as reaction rate and pH controllers, for toxic anion or trace metal ion removal, as sensors, in bioreactors and in water treatment processes.
U.S. Pat. Nos. 4,543,169; 4,414,090; 4,230,549; 4,107,005; 3,674,669; 3,427,206; 4,468,441; 4,339,473; 4,113,922; 4,012,303; and 3,556,965 assigned to RAI Research Corp. disclose various aspects of the manufacture and use of dialysis membranes.